--- The /64 stands for applications on 64-bit Windows operating system ---

COM/ActiveX/64:
This installs the COM/ActiveX (64-bit) version on your
machine.
For programming you may still need the 32-bit version. For instance, Visual Studio 2010 is a 32-bit application and when installed on a 64-bit Windows operating system will run under WOW64.

.NET/64: This
installs the .NET Assembly (64-bit) version on your
machine.
For programming you may still need the 32-bit version. For instance, Visual Studio 2010 is a 32-bit application and when installed on a 64-bit Windows operating system will run under WOW64.